Abstract
Purpose
To explore the relationship between physical activity (PA) and quality of life (QOL) among Hispanic and non-Hispanic white breast cancer (BC) cases and population-based controls from the New Mexico ‘Long-Term Quality of Life Study’.
Methods
Self-reported PA (low, moderate, vigorous MET hours/week) at baseline and follow-up interviews (12–15 years) were available for 391 cases and controls and modeled using multiple linear regressions with SF-36 mean composite scores for physical and mental health. The change in PA from baseline to follow-up and interactions with ethnicity were also examined. Models were adjusted for age at diagnosis/baseline interview, education, comorbidities, body mass index, and change in PA.
Results
PA intensities at each timepoint did not differ by case/control status; however, the change in vigorous PA was lower among cases (p = 0.03). At follow-up, low intensity PA increased mental health QOL scores among cases; however, the interaction between low intensity PA and ethnicity was statistically significant among controls indicating decreased mental health among Hispanics (p = 0.02). Change in moderate PA was associated with increased physical and mental health among cases (physical: β = 0.186, p = 0.008; mental: β = 0.225, p = 0.001) and controls (physical: β = 0.220, p < 0.0001; mental: β = 0.193, p = 0.002), when controlling for confounders.
Conclusion
Our results demonstrate that all levels of PA are important for mental health among BC cases, while activities of higher intensity are important for physical health among women overall. The statistical interaction observed between ethnicity and low intensity PA among controls for mental health warrants further research to provide a meaningful interpretation.
Keywords: Breast cancer, Cancer survivorship, Physical activity, Quality of life, Hispanic Americans
Introduction
In the United States, breast cancer (BC) remains the most common non-cutaneous cancer diagnosed among women, with an estimated 268,000 new cases in 2019 [1]. Breast cancer survivorship has increased due to advances in prophylactic screening and subsequent treatment(s), with approximately 2.5 million current survivors [2]. Generally, women surviving BC have a predicted 5- and 10-year survival rate at 93% and 80%, respectively [3]. However, incidence and mortality for BC varies significantly by ethnic group. Although Hispanic women share similar risk factors of non-Hispanic white (NHW) women, they have a 28% lower incidence rate [4]. In spite of this discrepancy, BC remains the leading cause of cancer death among Hispanic and NHW women living within the United States [4].
Previous studies have established obesity as a risk factor for both BC diagnosis [5, 6] and prognosis [7] among women and acts as a contributing factor to the development of a number of cancer treatment side effects [8–10]. To increase likelihood of survival, clinical trial interventions have focused on the impact that lifestyle modifications may have in improving these comorbidities, highlighting the role of regular physical activity (PA) of all intensities (low, moderate, vigorous) both during and after BC treatment [8, 11–13]. Previous studies have found that post-diagnosis PA was inversely associated with all-cause and BC mortality [14]. Specifically among this population, regular vigorous intensity PA exhibited 42% lower risk of all-cause mortality when compared with female BC survivors exercising at a low intensity [14]. Additionally, increased attention has been paid to the overall cancer experience (diagnosis to survivorship/death) and how it may be positively associated with, not only physiological health, but quality of life (QOL) [15, 16]. Thus, PA has been used to boost QOL over the course of BC treatment and survivorship, with highest minutes of PA per week reporting the greatest increases in QOL [17, 18]. For instance, Dibble and colleagues recently found that among NHW BC survivors, most women are not meeting weekly American College of Sports Medicine (ACSM) [19] exercise recommendations (150 min of moderate [3.0–5.9 METs], 75 min of vigorous [6.0 and higher METs], or a combination of the two), strengthened by positive relationships between regular PA and QOL domains [20]. In comparison to NHW survivors, Hispanic BC survivors are younger, less physically active, and experience larger short-term benefits of PA relating to QOL [21]. Additionally, obesity diagnosed prior to study enrollment among Hispanic BC survivors has been found to be associated with decreased mental and physical health up to 9 years following BC treatment [5]. Clinical trials have highlighted significant reductions in anxiety and improvements in perceived health among Hispanic BC survivors who regularly exercise [22, 23]. Although most Hispanic BC survivors may meet PA recommendations, it is not always indicative of the betterment of QOL but may be used in a supportive role for cancer care [24]. Yet, there has been little research that we are aware of, comparing the impact of changing PA levels over time on QOL among BC survivors and population-based controls, and furthermore by ethnicity.
To address the identified research gaps, we examined the relationship between PA and QOL domains among Hispanic and NHW BC survivors (cases) in addition to population-based controls from the ‘Long-Term Quality of Life’ Study (LTQOL), a 12- to 15-year follow-up study of BC cases and controls recruited from the New Mexico Women’s Health Study (1992–1994) [25, 26]. By comparing BC survivors to population-based controls without BC, we evaluated whether the relationships between PA, as measured by MET hours/week per intensity (low, moderate, vigorous) and several QOL domains are relevant to BC survivors and/or common to women of similar age without BC. We compared cases and controls to begin to understand their relationships with Hispanic ethnicity, PA intensities and QOL to further research disparities among this population. Therefore, we hypothesize that women with a history of BC will have a significantly different QOL with varying intensities of PA and that this relationship will differ by ethnicity.
Methods
Study population
The LTQOL follow-up study (2007–2011) was conducted within a mean time of 14.5 years from the date of BC diagnosis (cases) or date of selection (controls), among those who participated in the NMWHS (1992–1994) [25, 26]. The NMWHS was a state-wide population-based case–control study of BC in Hispanic and NHW women. The design of this study has been previously published [7, 25–28]. Briefly, cases included women diagnosed with a first primary incident BC ascertained through the New Mexico Tumor Registry (NMTR), a population-based tumor registry and a member of the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute (NCI). Women diagnosed with an invasive or in-situ breast carcinoma from January 1, 1992 through December 31, 1994, who were residents of New Mexico and who were between 30 and 74 years of age at diagnosis, were eligible. All identified Hispanic cases (n = 491) and approximately 33% of identified NHW cases (n = 493) selected using a stratified random selection process were eligible for inclusion. Population-based controls were selected using a modified random-digit dialing method and were frequency-matched to cases based on self-reported race/ethnicity, 5-year age group, residence within seven health planning districts. A total of 1,039 controls were eligible. A total of 339 Hispanic (69%) and 388 NHW (78%) cases and 391 Hispanic [76%] and 453 NHW [86%]) controls completed an in-person interview [26].
The LTQOL follow-up study
The LTQOL study was designed to address survival, recurrence, and specific dimensions of health-related QOL and assess covariates including self-reported age, race/ethnicity, clinical cancer characteristics, and cultural, social, behavioral and physiological factors. Of the 1506 NMWHS participants (baseline), a total of 321 died before follow-up, one had an inaccurate BC diagnosis, and 82 were considered ineligible for the LTQOL study due to non-cancer related issues (i.e., poor health, language barriers). Of the eligible and alive potential follow-up participants (N = 1244), 336 (27.0%) were lost to follow-up and 369 (29.6%) refused. A total of 457 women (187 cases, 270 controls) of the remaining 1,162 participants were included in the follow-up survey, of which approximately 96% completed the telephone interview (n = 1116). At the conclusion of the follow-up study, it was determined that 19 controls were diagnosed with incident BC after the NMWHS interview; however, six of the 19 were excluded due to a diagnosis of BC prior to 1992. Therefore, for the present analyses, 200 cases (69 Hispanic, 131 NHW) and 251 controls (79 Hispanic, 172 NHW) were eligible for study inclusion. For all participants, informed consent and Health Insurance Portability and Accountability (HIPAA) authorization (for those consenting to medical record review) were collected at the time of interview. The NMWHS baseline study and the LTQOL follow-up study were approved and monitored by the institutional review board (IRB) committees at the University of New Mexico and University of Louisville, respectively.
Data collection
Questionnaire
The LTQOL questionnaire collected data on the following: general health, physical and mental quality of life using SF-36 [29], diagnostic and treatment information, cancer screening practices, PA in metabolic equivalent (MET) values based on the 2011 Ainsworth Compendium of Physical Activities [30] and demographic information such as marital status, education, and employment, at both baseline and follow-up. The Charlson Index (CI) was used to categorize the number and impact of comorbid conditions reported by participants at follow-up, and is weighted, accounting for number and seriousness of comorbid conditions [31].
Quality of life (QOL)
The SF-36 Health Survey[29] measures eight health domains: physical functioning, bodily pain, role limitations due to physical health problems, role limitations due to personal or emotional problems, general mental health, social functioning, energy/fatigue, and general health perceptions [29]. The scores for each domain were combined to generate composite scores for mental (MCS = social functioning + role limitations due to personal or emotional problems + general mental health) and physical health (PCS = bodily pain + physical functioning + role limitations due to physical health problems + energy/fatigue scores). Individual domains and composite scores ranged from zero to 100, with higher scores representing better health quality. The reliability and validity of the SF-36 instrument has been documented in several diverse cancer survivor populations [32–35], but SF-36 scores must be interpreted in regard to cultural differences.
Physical activity (PA)
Physical activity was assessed using the questionnaire described above utilizing the same questions at baseline and follow-up. Self-reported PA (within the past month) was based on the following distinctions from the validated Ainsworth Compendium of Physical Activity [30]: (1) low-intensity MET hours/week (e.g., activity where one is walking at a quick pace), (2) moderate-intensity MET hours/week (e.g., carrying light loads, bicycling at a regular pace, etc., excluding walking), and (3) vigorous-intensity MET hours/week (e.g., running, calisthenics, fast bicycling, etc.) [19]. Questions asked number of activities at each PA intensity level (by day, week, month) and the number of hours spent doing each activity [19]. Total MET hours were calculated for each PA intensity level using the 2011 Ainsworth Compendium of Physical Activities MET formulaic equations [30]. True change in low-, moderate-, and vigorous-intensity MET hours/week were calculated using the difference in MET hours/week from baseline to follow-up.
Statistical methods
Data analysis was limited to women with PA and QOL composite values (Cases n = 197; Controls n = 194). All study variables were evaluated using descriptive statistics and graphical techniques to assess distributional assumptions and to identify outliers. In preliminary analyses to identify covariates of interests, demographic, clinical, and other variables collected at baseline and follow-up interviews were assessed using analyses of variance (ANOVA) and independent t-tests. Pearson correlations were also used to determine covariate status. The following variables were evaluated: age at baseline (years), age at follow-up (years), age at BC diagnosis (years), baseline body mass index (BMI), ethnicity, education level (less than high school, high school graduate, greater than high school), and change in low, moderate, and vigorous MET hours/week from baseline to follow-up. The CI score for presence of comorbid conditions was categorized into four groups: none (no comorbid conditions), low (1–2 comorbid conditions), moderate (3–4 comorbid conditions), and high (5 + comorbid conditions). The type of BC treatment(s) (no surgery; surgery + radiation + chemotherapy; surgery + radiation; surgery + chemotherapy; surgery only) was also considered as a potential covariate for cases only; although it was not found to be a significant covariate for associations between PA and QOL subscales and was not retained in the models. Descriptive statistics of the study sample were compared by case/control status for categorial and continuous variables using chi-square tests and t-tests, respectively.
Multiple linear regression models were used to assess the relationship between PA intensity levels in MET hours/week (low: < 3, moderate: ≤ 3 to < 6, vigorous: ≥ 6) and QOL composite scores (PCS, MCS) at follow-up. To examine the effect of PA intensity level on physical and mental health QOL by ethnicity among cases and controls, an interaction term was created for each change (Δ) in PA intensity level combined with ethnicity within appropriate models (Δ low-intensity PA × ethnicity, Δ moderate-intensity PA × ethnicity, Δ vigorous-intensity PA × ethnicity). Age at baseline and education were significantly different between cases and controls and were adjusted for in reduced models. Fully adjusted models included the following additional variables: CI score, race/ethnicity (Hispanic; NHW), baseline BMI, and change in PA intensity (MET hours/week from baseline to follow-up). All analyses were performed using the IBM Statistical Package for the Social Sciences (SPSS) Version 26 [36].
Results
Relevant demographic, health, and clinical BC characteristics are depicted by case/control status in Table 1. Age at the time of diagnosis (cases; M = 49.2, SD = 9.4) or initial interview (controls; M = 49.7, SD = 10.4) was not statistically different by case and controls (p = 0.55) (Table 1). Among cases, most BC survivors reported having localized BC (n = 109, 54.5%) and having no surgery (n = 67, 33.5%). Educational attainment differed between cases and controls (p = 0.04), but in both groups the majority of participants reported having greater than a high school education. Cases and controls did not differ on BMI status (baseline or follow-up), change in BMI, either MCS or PCS, comorbid conditions, or any of the PA typologies. These groups did differ on the change in vigorous-intensity MET hours/week (p = 0.03) (Table 1).
Table 1.
Characteristics of the study sample, stratified by case–control status, LTQOL
| Cases/survivors n = 197 |
Controls n = 194 |
X2-p value | |
|---|---|---|---|
| N (%) | N (%) | ||
| Ethnicity | |||
| Hispanic | 69 (34.5) | 79 (31.5) | 0.49 |
| NHW | 131 (65.5) | 172 (68.5) | |
| Education level at baseline | |||
| Lower than high school | 11 (5.5) | 6 (2.4) | 0.04 |
| High school or GED | 55 (27.5) | 52 (20.7) | |
| Greater than high school | 134 (67.0) | 192 (76.5) | |
| Baseline: BMI | |||
| <25 (normal weight or under) | 115 (57.5) | 137 (54.6) | 0.66 |
| ≥30 (overweight or obese) | 85 (42.5) | 110 (43.8) | |
| Follow-up: BMI | |||
| <25 (normal weight or under) | 81 (40.5) | 99 (39.4) | 0.88 |
| ≥30 (overweight or obese) | 117 (58.5) | 147 (58.6) | |
| Charlson Index comorbid conditions | |||
| None (0) | 71 (35.5) | 111 (44.2) | 0.18 |
| Low (1–2 conditions) | 107 (53.5) | 113 (45.0) | |
| Moderate (3–4 conditions) | 18 (9.0) | 19 (7.6) | |
| High (5 + conditions) | 3 (1.5) | 7 (2.8) | |
| Cancer diagnosis summary | |||
| In situ | 38 (19.0) | – | – |
| Localized | 109 (54.5) | – | |
| Regional/distant | 51 (25.5) | – | |
| Treatment for breast cancer | |||
| No surgery | 67 (33.5) | – | – |
| Surgery, radiation, and chemotherapy | 46 (23.0) | – | |
| Surgery and chemotherapy | 31 (15.5) | – | |
| Surgery and radiation | 53 (26.5) | – | |
| Surgery only | 2 (1.0) | – | |
| Mean (SD) | Mean (SD) | t-test (p) | |
| Age at time of diagnosis/interview (years) | 49.2 (9.42) | 49.7 (10.4) | 0.55 |
| Change in BMI | 1.44 (3.76) | 1.65 (3.98) | 0.56 |
| Physical composite score (PCS) | 72.5 (22.3) | 74.0 (21.5) | 0.46 |
| Mental composite score (MCS) | 75.7 (19.7) | 77.4 (19.4) | 0.35 |
| Baseline: low-intensity MET h/week | 0 (0.0) | 0.10 (1.52) | 0.34 |
| Follow-up: low-intensity MET h/week | 7.06 (10.4) | 8.86 (13.0) | 0.71 |
| Baseline: moderate-intensity MET h/week | 44.9 (33.6) | 43.9 (28.2) | 0.64 |
| Follow-up: moderate-intensity MET h/week | 14.5 (16.7) | 16.1 (22.4) | 0.12 |
| Baseline: vigorous-intensity MET h/week | 7.13 (14.6) | 6.50 (13.6) | 0.40 |
| Follow-up: vigorous-intensity MET h/week | 10.3 (19.9) | 14.7 (28.6) | 0.07 |
| Change in low-intensity MET h/week | 7.16 (10.4) | 8.81 (13.1) | 0.16 |
| Change in moderate-intensity MET h/week | 30.3 (35.6) | 27.2 (35.4) | 0.38 |
| Change in vigorous-intensity MET h/week | 3.27 (19.2) | 8.33 (27.1) | 0.03 |
BMI body mass index. LTQOL long-term quality of life, MET metabolic equivalent tasks, NHW non-Hispanic white
Bold font indicates p < 0.05
Findings among moderate- and vigorous-intensity PA differed between cases and controls. Moderate-intensity PA was a significant predictor of better physical QOL at both baseline and follow-up among cases (Baseline: β = 0.274, SE = 0.084, p = 0.030; Follow-up: β = 0.151, SE = 0.088, p = 0.020) and controls (Baseline: β = 0.201, SE = 0.061, p = 0.012; Follow-up: β = 0.199, SE = 0.066, p = 0.003) (Table 2). There were significant differences between NHW and Hispanic controls and their interaction with moderate-intensity PA (β = 0.360, SE = 0.103, p = 0.026), but this finding was not significant among cases (Table 2). Furthermore, vigorous-intensity PA was significantly associated with better physical QOL at baseline among controls (β = 0.187, SE = 0.084, p = 0.001) but not among cases. At follow-up, vigorous-intensity PA predicted physical QOL among cases (β = 0.166, SE = 0.069, p = 0.007) and controls (β = 0.434, SE = 0.164, p = 0.043) (Table 2). The interaction terms between low and vigorous MET hours/week and ethnicity were not significant.
Table 2.
Associations between low, moderate, and vigorous physical activity MET hours/week at baseline and follow-up and physical and mental QOL among women from the LTQOL study
| Cases (n = 197) | Controls (n = 194) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Low intensity n = 197 |
Moderate intensity n = 197 |
Vigorous intensity n = 197 |
Low intensity n = 194 |
Moderate intensity n = 194 |
Vigorous intensity n = 194 |
|||||||
| Parameter estimates (SE) | p-value | Parameter estimates (SE) | p-value | Parameter estimates (SE) | p-value | Parameter estimates (SE) | p-value | Parameter estimates (SE) | p-value | Parameter estimates (SE) | p-value | |
| Quality of life: SF-36 physical health | ||||||||||||
| Baseline METs/week | ||||||||||||
| No interaction | ||||||||||||
| METs/week | 0.0 (0.0) | Invariable | 0.274 (0.084) | 0.030 | −0.044 (0.094) | 0.474 | 0.045 (0.760) | 0.408 | 0.201 (0.061) | 0.012 | 0.187 (0.084) | 0.001 |
| Hispanic ethnicity | 0.070 (3.15) | 0.298 | 0.045 (3.13) | 0.506 | 0.064 (0.039) | 0.344 | 0.060 (2.53) | 0.149 | 0.069 (2.62) | 0.206 | 0.065 (2.43) | 0.230 |
| Follow-up METs/week | ||||||||||||
| No interaction | ||||||||||||
| METs/week | 0.632 (1.67) | 0.376 | 0.151 (0.088) | 0.020 | 0.166 (0.069) | 0.007 | 0.381 (0.699) | 0.359 | 0.199 (0.066) | 0.003 | 0.150 (0.041) | 0.006 |
| Hispanic ethnicity | 0.066 (3.16) | 0.331 | 0.045 (3.12) | 0.503 | 0.044 (3.10) | 0.503 | 0.061 (2.53) | 0.143 | 0.074 (2.51) | 0.177 | 0.059 (2.51) | 0.280 |
| Quality of life: SF-36 mental health | ||||||||||||
| Baseline METs/week | ||||||||||||
| No interaction | ||||||||||||
| METs/week | 0.0 (0.0) | Invariable | 0.287 (0.076) | 0.027 | 0.066 (0.086) | 0.299 | −0.047 (0.776) | 0.441 | 0.142 (0.063) | 0.120 | .154 (0.087) | 0.013 |
| Hispanic ethnicity | 0.065 (2.86) | .347 | .049 (2.85) | .477 | .059 (2.87) | 0.394 | 0.059 (2.60) | .345 | 0.064 (2.60) | 0.306 | 0.061 (2.57) | 0.322 |
| Follow-up METs/wk | ||||||||||||
| No interaction | ||||||||||||
| METs/week | 0.131 (0.119) | 0.036 | 0.149 (0.080) | 0.027 | 0.152 (0.063) | 0.017 | 0.062 (0.092) | 0.176 | 0.181 (0.068) | 0.019 | 0.147 (0.043) | 0.017 |
| Hispanic ethnicity | 0.060 (2.84) | 0.336 | 0.060 (2.85) | 0.466 | 0.051 (2.64) | 0.458 | 0.063 (2.60) | 0.313 | 0.070 (2.69) | 0.261 | 0.056 (2.50) | 0.364 |
Missing values for MET hours/week: Baseline—low (5), moderate (3), vigorous (6); Follow-up – low (19), moderate (6), vigorous (6)
Standardized beta coefficients are reported
Models adjusted for age at baseline, ethnicity, BMI, education, Charlson index, change in appropriate PA. Missing values: Education (1); Charlson Index (2); Change in PA MET hours/week (10)
METs metabolic equivalent tasks, SE standard error
Bolded estimates are statistically significant (p < 0.05)
For controls, low intensity PA at baseline (β = −5.35, SE = 26.5, p = 0.010) and the interaction between ethnicity and low-intensity PA (β = 5.31, SE = 13.3, p = 0.011) were significant predictors of poorer mental health QOL among controls at follow-up; these results were not observed in cases (Table 2). In contrast, low-intensity PA at follow-up (β = 0.552, SE = 0.320, p = 0.009) and ethnicity (β = 0.154, SE = 3.05, p = 0.036) were predictors of increased mental health QOL. Interestingly, among controls, the interaction of low-intensity PA and being Hispanic (β = − 0.496, SE = 0.187, p = 0.020) was associated with poor mental health QOL. Moderate-intensity PA at baseline was a positive significant predictor among cases (β = 0.287, SE = 0.076, p = 0.027), but not among controls. However, both groups exhibited positive significant relationships between mental health QOL and moderate-intensity PA levels at follow-up (cases: β = 0.149, SE = 0.080, p = 0.027; controls: β = 0.181, SE = 0.068, p = 0.019) (Table 2). Associations between mental health QOL and vigorous-intensity PA at baseline were not similar; where this relationship was significant among controls (β = 0.154, SE = 0.087, p = 0.013) but not among cases. In contrast, vigorous-intensity PA at follow-up was a significant predictor of mental health QOL among controls and cases (β = 0.147 and β = 0.152, respectively, p = 0.017).
Adjusted associations were also modeled examining the change in PA intensity level from baseline to follow-up predicting physical and mental health QOL, stratified by case/control status. Among cases, the change in vigorous-intensity PA was associated with an increase in physical QOL at follow-up (β = 0.163, SE = 0.003, p = 0.009). Additionally, moderate-intensity PA change was associated with increased mental health QOL at follow-up among cases (β = 0.194, SE = 0.002, p = 0.004) (Table 3). There were no significant relationships among controls.
Table 3.
Linear regressions comparing changes in PA intensity MET h/week from baseline to follow-up to physical and mental health QOL among cases and controls
| Physical QOL | Mental health QOL | |||||
|---|---|---|---|---|---|---|
| Parameter estimates | Standard error (SE) | p-value | Parameter estimates | Standard error (SE) | p-value | |
| Cases (n = 197) | ||||||
| Charge in low intensity | 0.069 | 0.005 | 0.266 | 0.127 | 0.006 | 0.062 |
| Charge in moderate intensity | 0.073 | 0.002 | 0.244 | 0.194 | 0.002 | 0.004 |
| Charge in vigorous intensity | 0.163 | 0.003 | 0.009 | 0.039 | 0.003 | 0.571 |
| Controls (n = 194) | ||||||
| Charge in low intensity | 0.066 | 0.004 | 0.196 | 0.070 | 0.005 | 0.274 |
| Charge in moderate intensity | 0.092 | 0.001 | 0.071 | 0.124 | 0.002 | 0.053 |
| Charge in vigorous intensity | 0.042 | 0.002 | 0.410 | 0.058 | 0.002 | 0.361 |
METs Metabolic equivalent tasks, SE standard error
Missing values: baseline—low (5), moderate (3), vigorous (6); Follow-up—low (19), moderate (6), vigorous (6)
Missing values: Education (1); Charlson Index (2)
Standardized beta coefficients are reported
Models adjusted for age at baseline, ethnicity, BMI at baseline, education, and Charlson index
Bolded estimates are statistically significant (p < 0.05)
Discussion
The current study is one of the few [21] to examine the associations between varying intensity levels of PA and QOL among long-term Hispanic and NHW BC survivors and population-based controls of similar age and race/ethnicity. Although previous research has found that NHW survivors are more likely to meet exercise recommendations set forth by the ACSM [9], NHW and Hispanic women with a history of BC were similar in meeting PA recommendations per week at both baseline and follow-up. The current study showed that New Mexican Hispanic BC cases reported more hours of vigorous-intensity PA at baseline and more hours across all PA intensity levels at follow-up. Overall, being physically active was associated with increased physical QOL at follow-up among controls. Findings for physical QOL scores varied by PA influenced intensity levels and data collection timepoint as well as by case–control status. While low-intensity PA was not a significant predictor, moderate- and vigorous-intensity PA at baseline and follow-up was associated with increased physical QOL among cases and controls. Findings were similar for mental health QOL scores. Higher levels of PA are important for physical and mental QOL, especially among BC cases. Similarly, change in any type of PA from baseline to follow-up was positively associated with increased physical QOL, while moderate PA change reflected increases in mental health QOL among cases. This is an interesting finding, as it shows PA of any intensity is generally associated with increases in mental health QOL, while physical QOL may be linked with higher levels of PA.
Physical activity remains an important aspect of the cancer survivorship experience [11–13, 20, 27], by influencing health-related QOL, as our study has shown. Although some literature has shown that comorbidities are more prevalent among survivors of BC compared to women without BC [37–39], this has not been found in the current study [40]. Being physically active may decrease the burden of subsequent comorbid conditions [8–10, 27, 37, 41, 42] and increase long-term survival [7]. By accounting for comorbidities in adjusted models, mental health and physical QOL were attenuated among cases and controls, indicating the presence of comorbid conditions is a strong confounder in this association. While the relationship between PA and QOL among BC survivors is complex [43–45], these results may suggest that there is more to healthy survivorship than healthy weight maintainence [46]. Our findings support some previous literature in identifying moderate and vigorous PA as promoting weight loss and staving the incidence of additional comorbid conditions found within the general population [6]. Coupled with what we know about BC survivorship and the impact of comorbid conditions, our findings may begin to explain how survivors require supplementary PA to exhibit the physical benefits for QOL.
Interestingly, the directionality between low-intensity PA and the interaction of low-intensity PA and ethnicity among controls switched from baseline (positive association) to follow-up (negative association). These findings may possibly suggest that there may be contextual factors that were not assessed that may influence the relationship between mental health QOL, PA, ethnicity, and time among women without BC. Again, not all intensities of PA were found to promote mental health QOL. At baseline, only moderate PA predicted mental health QOL among cases. Most previous literature has focused on QOL overall and PA, not differentiating between physical and mental health components of QOL in cancer survivors and matched controls [47, 48]. More research is needed to understand the impact of PA, and objective measurement of, and their intensities on mental health QOL specifically, to discern these relationships.
Hispanic cases in our study were more likely to report higher physical health QOL at follow-up, possibly due to unique cultural backgrounds, despite exercising at a low intensity than NHW survivors. This supports what previous literature has found, that regular PA both increases the physical fitness profile and physical QOL among adults, but the current study does not support the same notion among BC survivors [49]. Among previous literature, Hispanic women generally have reported more household chores in comparison to NHW women [49, 50], so this may explain the differences in PA intensities at each timepoints. These findings might also suggest that not all MET activities are equal, and that for instance, doing household chores versus a gym-type exercise may not provide the same physical health benefits [51, 52]. Previous literature may also support determination of such PA, as “occupational” PA (e.g., lifting, housework, etc.) may provide less benefit on QOL than “non-occupational” or “leisure” PA [51, 52]. These findings suggest that there may be a more complex relationship between the social or cultural lives of Hispanic BC survivors, PA, and QOL, even years into survivorship, which has not been supported by the current study. Supportive patterns occurred among controls, showing that Hispanic controls were more likely to exhibit higher mental health QOL at follow-up, similarly backed by previous literature [53]. However, this does not explain the ethnic differences found; that Hispanic controls differed from NHW controls on these outcomes. Not only is additional research needed in the long-term care of Hispanic BC survivors and healthy Hispanic female populations as well, but it also appears as though there are other contributing factors in addition to demographics, PA, and mental health QOL.
While our findings provide important information for BC survivors and those who provide follow-up care to BC survivors, these results must be interpreted in light of the current study’s limitations. Despite finding some support between PA and physical and mental health QOL, a larger sample size would have increased the statistical power of the analyses and allowed for sample stratification on a deeper level. Given the response rate of 39%, this follow-up study is not representative of the original NHWHS. Due to a small sample size, some of the statistically significant results may be artifacts in the data and not be biologically meaningful.
Long-term cancer survivors have been described as survivors who are 5 years or more post-diagnosis [54]. In the current study, however, our case sample reported at least three times the survivorship time, as much as 72% of cases have 14 or more years of survivorship [27]. Despite finding some support between several PA intensities, physical, and mental health QOL, a more concrete measure of PA may have been beneficial. PA is a complex variable with many different activities contributing to energy expenditure, and within an ethnic frame, the assembly of these activities into total METs/week is likely socioeconomically, culturally, and contextually different. The current study implemented a brief PA measure, which was shorter at baseline than at follow-up. For instance, the use of a longer instrument or especially, an accelerometer may have proven useful in objectively measuring different PA intensities as a physiological measure instead of using self-report data for both PA and QOL. Additionally, we would have liked to adjust for relevant covariates such as sitting or sedentary time, possible non-cancer related treatments and procedures, medication use for comorbidities, or the severity of comorbid conditions, but the questionnaire did not include these variables. Based on results from systematic reviews, very few QOL studies have included Hispanic long-term cancer survivors in comparison to population-based, age and ethnicity matched controls [58, 59]. Our analyses have suggested that ethnicity, among cases and controls, was associated in combination with certain intensities of PA with physical and mental health QOL. However, our findings may not be generalizable to all NHW and Hispanic BC survivors but may be beneficial for those within these groups who have long-term survivorship and those who live within the Southwest region of the United States, as these populations may be different, both in terms of culture and ancestry, from other Hispanic or Latino populations elsewhere.
Conclusions
Despite these limitations, the current study presents findings that are based on an examination of the relationship between PA intensity levels and QOL among an ethnically diverse population of long-term BC survivors and population-based controls. Our results indicate that PA between baseline and follow-up interviews was associated with variable physical and mental health QOL among the study population, regardless of case–control status. Our findings can be used to enhance clinical communication about the importance of PA for improving QOL, even at low levels, among all women as they age, regardless of BC history. Results were variable by ethnicity and more information and research are needed for meaningful interpretation. Therefore, our findings provide an insight into a diverse population of BC survivors and controls and the impact of PA on the physical and mental aspects of long-term QOL.
Funding
This work was supported by the following grants: NIH/NCI, R01-CA55730 The New Mexico Women’s Health Study; NIH/NCI 1 R01-CA105266 Ethnicity, Breast Cancer Recurrence and Long-Term Quality of Life; Susan G. Komen Breast Cancer Disparities Epidemiology Research Training Program, Grant KG090926. KD received research support from the National Cancer Institute Cancer Epidemiology, Prevention, and Control Training Program (T32CA009314).
Abbreviations
- LTQOL
Long-Term Quality of Life Study
- MET
Metabolic equivalent
- NMTR
New Mexico Tumor Registry
- NMWHS
New Mexico Women’s Health Study
- NHW
Non-Hispanic white
- PA
Physical activity
- QOL
Quality of life
- SEER
Surveillance, Epidemiology, and End Results
Footnotes
Code availability The code generated and implemented during the current study are available from the corresponding author on reasonable request.
Conflict of interest The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The authors have no conflicts of interest to report.
Data availability
The datasets generated during and/or analyzed during the current study are available from the Principal Investigator of the study on reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets generated during and/or analyzed during the current study are available from the Principal Investigator of the study on reasonable request.